Na transport across a preparation of sheep omasum was studied. All tissues exhibited a serosa-positive short-circuit current (I_sc), with a range of 1-4 µeq · h¹ · cm². A Michaelis-Menten-type kinetic was found between the Na concentration and the I_sc (Michaelis-Menten constant for transport of Na = 6.7 mM; maximal transport capacity of Na = 4.16 µeq · h¹ · cm²). Mucosal amiloride (1 mM), phenamil (1 or 10 µ), or serosal aldosterone (1 µM for 6 h) did not change I_sc. Removal of divalent cations (Ca and Mg) enhanced I_sc considerably from 2.61 ± 0.24 to a peak value of 11.18 ± 1.1 µeq · h¹ · cm². The peak I_sc (overshoot) immediately declined to a plateau I_sc of ~6-7 µeq · h¹ · cm². Na flux measurements showed a close correlation between changes in I_sc and Na transport. Transepithelial studies demonstrated that K, Cs, Rb, and Li are transported, indicating putative nonselective cation channels, which are inhibited by divalent cations (including Ca, Mg, Sr, Ba) and by (trivalent) La. Intracellular microelectrode recordings from the luminal side clearly showed changes of voltage divider ratio when mucosal divalent cations were removed. The obtained data support the assumption of a distinct electrogenic Na transport mechanism in sheep omasum.

calcium-sensitive sodium transport; nonselective cation channel; Ussing chamber; microelectrodes; apical conductance

This article has been cited by other articles:

				M. S. Awayda, A. Bengrine, N. A. Tobey, J. D. Stockand, and R. C. Orlando Nonselective cation transport in native esophageal epithelia Am J Physiol Cell Physiol, August 1, 2004; 287(2): C395 - C402. [Abstract] [Full Text] [PDF]